Tender Greens, with 28 restaurants on the East and West coasts, is one of a growing number of eateries that are either shunning cash and only accepting credit and debit cards and contactless payment systems, like Apple Pay, or experimenting with the strategy.

While no one has kept a running count of restaurants adopting the cashless policy, interest is clearly rising. A 2016 Federal Reserve study found the number of non-cash payments — including credit and debit cards — totaled 144 billion in 2015, having grown 5.3% annually between 2012 and 2015

Sweetgreen, another salad chain on the coasts and part of the Midwest, and some independent restaurants have adopted the same policy. Two national chains are exploring it.

In January, Starbucks made one of its shops in its hometown of Seattle cashless, and Shake Shack, the gourmet hamburger chain, began testing cashless kiosks at its Astor Place restaurant in New York City in October. Both chains declined to discuss their experiments.

Restaurant owners say ordering is faster from customers who slap down plastic instead of dollars, cutting a few seconds out of the process. But most of the benefits appear to accrue to the restaurants: less time taken counting bills, reduced pilferage, no armored-car fees or fear of stickups.

It's a risky strategy. For starters, upscale Millennials — among the most coveted of diners because of their youth and affluence — prefer to pay in cash, according to Bankrate.com data. Also, more than a third of Americans between the ages of 18 and 37 do not have a credit card.

For customers, patronizing restaurants that don't take cash means one less payment option when they need a quick meal during an all-too-short lunch hour. Plus, it raises questions about whether it discriminates against cardless teens and the poor.

Miah Daughtery took to social media in the fall after encountering the policy at a Sweetgreen restaurant in Washington, D.C.

"There’s an assumption that people have a credit or debit card on them. If I didn’t, does that mean I wouldn’t be able to get lunch?" said Daughtery, 38.

She added that her parents grew up in an era when cash was king, so they would potentially be out of luck, too.

A committee in Chicago is weighing Alderman Edward Burke's proposed requirement that merchants accept cash. Massachusetts has had a Discrimination Against Cash Buyers rule on the books since 1978.

"Most people who use cash are people who don’t have access to a bank account and are lower income," said Lana Swartz, co-editor of the book Paid: Tales of Dongles, Checks, and Other Money Stuff. "One of the cornerstones of American capitalism is everyone’s money is equal."

Cashless businesses point out customers usually have many choices when it comes to where they shop. And when someone, such as a homeless person or a young teen, doesn't have a credit or debit card, some restaurants say they've given out their share of free meals to tough-luck cases. give them a break and let them eat for free.

Tender Greens says it cut 10 seconds of ordering time by going cashless. "A customer doesn't have to wait as long. It makes us competitive," President Denyelle Bruno said.

Señor Sisig, a fleet of five Filipino-fusion food trucks in the San Francisco area, counts higher tips and less hassle as the benefits of having gone cashless Jan. 1.

It's "frustrating when I have valuable employees just counting cash," founder Evan Kidera said, calculating it gobbled up more than 40 hours in total a week. "This was a way to get them back doing what they're good at, which was food and service."

Plus, fewer customers were paying in cash anyway, having fallen from about 70% in 2010 to 19% before the change.

So far, though, the giants of the fast-food world remain unconvinced.

McDonald's spokeswoman Andrea Abate said the chain is "always looking to make things easier for our guests."

Paul Murray, the Dunkin' Brands director of digital experience, explained that "they can pay the way they want."